Camera capable of varying size of image plane

ABSTRACT

In a camera of the kind arranged to obtain an object image through a photo-taking lens at an arbitrary image plane size on a photosensitive surface by using an image plane size varying member, either the nearest shootable distance of the photo-taking lens is arranged to become shorter than the normally nearest shootable distance or the magnification varying range of the power varying part of the photo-taking lens is arranged to be expanded on the wide-angle side, as the diagonal length of the image plane size becomes shorter.

This application is a continuation of prior application Ser. No.08/300,852 filed on Sep. 6, 1994, which is a continuation of applicationSer. No. 07/963,730 filed on Oct. 20, 1992, both now abandoned.

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention relates to a camera having means for varying the imageplane size thereof and, more particularly, to a camera such as a 35 mmfilm camera, a video camera or the like arranged to be capable of takingshots with the size of its image plane varied through optical orelectrical means to attain a spurious power varying effect, a panoramicshot effect, an effect of change-over from a full size to a half size,etc., and also to enhance photo-taking lens specifications.

2. Description of the Related Art

Some of the known 35 mm film cameras or video cameras have heretoforebeen provided with image plane size varying means for variously changingthe image plane size through optical means, mechanical or electricalmeans in taking shots.

Some 35 mm film cameras, for example, have been arranged to be of thefollowing types:

(a) A type arranged to attain an image plane size change-over effect bymoving light-shielding members to partly cover the aperture of anexposure-range-defining mask on the left and right sides of the aperturein such a way as to change the image plane from a full size (36 mm×24mm) over to a vertically oblong half size (17 mm×24 mm) and vice versa.

(b) A type arranged to attain a panorama effect by movinglight-shielding members to partly cover the aperture of the mask in thevertical directions of the aperture in such a way as to change the imageplane from the full size over to a laterally oblong panorama size.

(c) Another type arranged to attain a spurious power varying effect bychanging (reducing) the image plane size in an analog manner with anaperture-diameter-varying member disposed in front of the film surface.

These cameras of the kind having the image plane size varying means arearranged to simply change the effective aperture of the mask accordingto the picture taking conditions by using a full size film.

Meanwhile, photo-taking lenses for use in the 35 mm film cameras orvideo cameras are arranged to perform a focusing action by moving eithera part of or the whole of the lens along an optical axis as a shootingdistance (object distance) changes. At that time, if the object distanceis shorter than the nearest shootable object distance set at the time ofdesigning, a luminous flux that would otherwise be incident on theperipheral part of the image plane is completely eclipsed by theaperture diaphragm or the edge of the photo-taking lens to hindershooting.

In other words, the nearest shootable object distance of the camera isgenerally restricted by the size of the whole lens system, the size ofthe frontmost lens diameter or the aperture diameter of the lens.

In a case where a zoom lens is employed as the photo-taking lens, when aluminous flux otherwise would be incident on the peripheral part of theimage plane with the lens in a certain zoom position on the wide-angleside of the lens, the luminous flux might be completely eclipsed by therestriction of the effective diameter of the lens. The zoom position onthe wide-angle side (a wide-angle end) of the lens is thus determinedpartly by the restriction of the effective diameter of the lens. Thistendency is salient particularly in a case where a photo-taking lenshaving a power varying part is used for a lens-shutter type camera.

SUMMARY OF THE INVENTION

It is a first object of this invention to lessen optical restrictionswhich are imposed on the optical specifications for the photo-takinglens of a camera to hinder changes in the specifications, in attainingvarious special shooting effects by varying the image plane size on aphotosensitive surface, such as a reduction in the nearest objectdistance and a further increase in the shooting angle of view (for anultra-wide angle) on the wide-angle side of the lens, if the lens is azoom lens.

It is a second object of this invention to provide a camera having imageplane size varying means which is arranged to lessen the opticalrestrictions.

It is a third object of the invention to provide a camera having imageplane size varying means which is arranged to be capable of obtaining anobject image at a desired image plane size on a photosensitive surfacethrough a photo-taking lens, wherein the photo-taking lens is arrangedto make its nearest shootable distance shorter when the diagonal lengthof the image plane is short than when the diagonal length is long.

It is a fourth object of the invention to provide a camera having imageplane size varying means which is arranged to be capable of obtaining anobject image at a desired image plane size on a photosensitive surfaceby a photo-taking lens which has a power varying part, wherein the powervarying range of the power varying part is arranged to be furtherexpandable on a wide-angle side when the diagonal length of the imageplane is short than when the diagonal length is long.

These and further objects and features of the invention will becomeapparent from the following detailed description of embodiments thereoftaken in conjunction with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIGS. 1A, 1B and 1C are sectional views showing the optical system of afirst embodiment of the invention.

FIG. 2 shows an optical path for the nearest object distance of theconventional photo-taking lens.

FIG. 3 is a block diagram showing the system arrangement of the firstembodiment of the invention.

FIG. 4 is a flow chart showing the operation of the first embodiment ofthe invention.

FIGS. 5A, 5B and 5C are sectional views of the optical system of asecond embodiment of the invention.

FIG. 6 is a block diagram showing the system arrangement of the secondembodiment of the invention.

FIGS. 7A and 7B are sectional views showing the optical system of athird embodiment of the invention.

FIGS. 8A to 8D show the layout of the optical system of a fourthembodiment of the invention as a thin-lens system.

FIGS. 9A and 9B are sectional views showing the optical system of afifth embodiment of the invention.

FIG. 10 is a block diagram showing the system arrangement of anotherembodiment of the invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

FIGS. 1A, 1B and 1C show a first embodiment of the invention. In thecase of this embodiment, the nearest shootable object distance isarranged to be made shorter by moving (drawing out) the focusing part ofthe photo-taking lens to a greater extent when the image plane size isreduced (when the diagonal line D of the image plane is shortened) for aspecial shooting effect than when the image plane size is large.

In these figures, reference numeral 1 denotes a photo-taking lens. Afocusing action is performed by moving the whole lens 1. Aphotosensitive surface 2 is made of, for example, a 35 mm silver-halidefilm. A diaphragm 3 is provided for controlling the amount of exposure.A mask 4 is provided for image plane size varying means 5 and isdisposed in front of the photosensitive surface 2. The photo-taking lens1 is normally composed of a plurality of lens elements. The casing ofthe camera is omitted from the illustration.

FIGS. 1A and 1B show the embodiment as having the image plane in itsfull size. In the case of FIG. 1A, the optical path is shown as in astate of having the photo-taking lens 1 focused on an object located atan infinity distance. FIG. 1B shows the optical path as in a state ofhaving the photo-taking lens 1 focused on an object located at thenearest object distance L1. FIG. 1C shows the embodiment as having theimage plane size on the photosensitive surface 2 reduced by the mask 4of the image plane size varying means. In the case of FIG. 1C, theoptical path is in a state of having the photo-taking lens 1 focused foran object distance L2 which is shorter than the object distance L1 as aresult of drawing out the photo-taking lens 1 further forward on theobject side than in the case of FIG. 1B. An adequate image is obtainableeven with the photo-taking lens 1 drawn out further forward. The reasonfor this is as follows:

When the photo-taking lens 1 is focused on an infinity distance objectas shown in FIG. 1A, a luminous flux L2a incident on a peripheral part2a of the image plane passes the diaphragm 3 in a relatively largequantity even when the aperture of the diaphragm 3 is reduced to a smallvalue.

When the photo-taking lens 1 is drawn out from its position of FIG. 1Ato be focused on an object located at the object distance L1 as shown inFIG. 1B, a luminous flux L2b incident on the peripheral part 2a of theimage plane is still allowed, in this instance, to pass the diaphragm 3in a quantity sufficient for an exposure, although it is somewhateclipsed by the photo-taking lens 1 and the diaphragm 3. In thisinstance, even if the diaphragm 3 is stopped down to a smaller aperture,some amount of luminous flux is still allowed to pass the diaphragm 3.Therefore, even if the diaphragm 3 is stopped down while focusing on anobject located at the object distance L1, a luminous flux falls on theperipheral part 2a of the image plane to allow taking a shot of anobject located at the nearest distance.

In a case where the photo-taking lens 1 is drawn out further from itsposition shown in FIG. 1B to be focused on an object located at anotherobject distance L2 which is shorter than the object distance L1, aluminous flux L2d incident on the peripheral part 2a of the image planeis allowed to pass the diaphragm 3, although only a slight amount of itis allowed to pass, when the diaphragm 3 is fully opened, as shown inFIG. 2. However, since the luminous flux L2d incident on the peripheralpart 2a of the image plane does not pass the central part of theaperture of the diaphragm 3, the luminous flux L2d is totally eclipsedby the diaphragm 3 when the diaphragm 3 is stopped down, so thatshooting becomes impossible.

On the contrary, in the event of a special shooting with the size of theimage plane reduced, as shown in FIG. 1C, the shooting angle of view isdecreased by the reduction in the image plane size. In that instance,therefore, a luminous flux incident on the peripheral part of the imageplane is eclipsed at a lesser rate by the photo taking lens 1 and thediaphragm 3.

Even in the case of FIG. 2, for example, the reduction in size of theimage plane as shown in FIG. 1C allows some amount of the luminous fluxincident on the peripheral part 2a of the image plane to pass thediaphragm 3 even when the diaphragm 3 is stopped down.

This embodiment has such a mechanism that, when the image plane is setat a smaller size to utilize the above-stated optical property, thefocusing part of the photo-taking lens can be moved to a greater extentby means of an interlocking mechanism than when the image plane is in alarger size. This arrangement effectively shortens the nearest shootableobject distance. More specifically, a drawing-out mechanism for thephoto-taking lens 1 is provided with an allowance part for increasingthe maximum drawing-out extent of the photo-taking lens 1 in associationwith a change to the smaller image plane size effected by the imageplane size varying means 5.

In a case where the camera has an automatic focusing mechanism, as willbe described later, a control circuit is arranged to allow the lensdrawing-out driving amount to exceed an amount allowable for the fullsize of the image plane when the image plane size is changed.

Further, in a case where this embodiment is applied to a video camera,the image plane size varying means is arranged to electrically vary theimage pickup range of an image sensor.

FIG. 3 shows the system arrangement of this embodiment. Referring toFIG. 3, a distance measuring circuit 11 operates as a part of a knownautomatic distance measuring means for measuring a distance L to anobject. A control circuit 12 is a microcomputer or the like. Theillustration includes a nearest-distance warning display circuit 13, arelease switch 31 of the camera, and a switch 32 for setting a panoramamode.

Further, with respect to the automatic distance measuring means, devicesof two different types are known. One is arranged to output the distanceto the object as a signal, while the other is arranged to output theamount of defocus of an objective lens as a signal. Either of thesedevices can be employed as the automatic distance measuring meansaccording to this invention.

Referring now to FIG. 4 which is a flow chart, the operation of thisembodiment is described as follows:

At a step #101: A check is made to find if the release switch 31 is on.If so, the flow of operation comes to a step #102. At the step #102: Adistance L to the object is measured by the distance measuring circuit11. At a step #103: A check is made for a special shooting mode, such asa panorama mode. The switch 32 is off when the image plane is in itsfull size. Therefore, if the switch 32 is off, the flow comes to a step#105. At the step #105: The object distance L is compared with thenearest object distance L1 shootable for the full image plane size. Ifthe distance L is found to be shorter than the distance L1, the flowcomes to a step #106 to give a nearest-distance warning before the flowcomes to a step for a release action.

In a case where the switch 32 is found to be on at the step #103 withthe panorama mode selected, the flow comes to a step #104. At the step#104: The distance L is compared with the nearest distance L2 shootablefor the panorama size of the image plane (L2<L1). If the distance L isfound to be shorter than the distance L2, the flow comes to the step#106 to give the nearest-distance warning before the flow comes to thestep for the release action.

As apparent from the foregoing, this embodiment is arranged to improvethe optical specifications of the photo-taking lens by varying thenearest shootable distance when the image plane size is changed.

FIGS. 5A, 5B and 5C show the optical system of a second embodiment ofthe invention. A zoom lens is employed as the photo-taking lens in thesecond embodiment. When the image plane size is reduced, that is, whenthe diagonal length of the image plane is shortened, for the purpose ofperforming a special shooting, an ultra-wide angle of view can beobtained by moving the power varying part of the zoom lens to a greaterextent along the optical axis for a power varying action than in thecase of a larger image plane size, in such a way as to expand ashootable angle of view.

In these figures, reference numeral 51 denotes the photo-taking lenswhich is composed of a zoom lens and is arranged, for example, in amanner as disclosed in Japanese Laid-Open Patent Application No. SHO57-201213. More specifically, the photo-taking lens 51 includes a firstlens group 51a which is of a positive refractive power, and a secondlens group 51b which is of a negative refractive power. Themagnification (power) of the zoom lens is variable from a rateobtainable at a wide-angle end position to a rate obtainable at atelephoto end position and vice verse by differentially moving the twolens groups 51a and 51b toward the object (image surface).

The illustrations include a photosensitive surface 2 which is made of,for example, a 35 mm silver-halide film, a diaphragm 53, and a mask 4for image plane size varying means. The mask 4 is disposed in front ofthe photosensitive surface 2.

FIGS. 5A and 5B show the image plane size of the photosensitive surface2 as in a full size. In FIG. 5A, the optical path is shown with the zoomlens 51 in the telephoto end position. In FIG. 5B, the optical path isshown with the zoom lens 51 in the wide-angle end position. FIG. 5Cshows a case wherein the image plane on the photosensitive surface 2 isreduced to a smaller size by the mask 4 for the image plane size varyingmeans 4. In FIG. 5C, the optical path is shown as in a state of having apower varying action performed in an ultra-wide-angle end zoom positionby moving the power varying part of the zoom lens 51 further on thewide-angle side than in the case of FIG. 5B.

In the wide-angle end zoom position as shown in FIG. 5B, a luminous fluxL55a incident on the peripheral part 2a of the image plane is blocked bythe edges of a lower part 55a of the first lens group 51a and an upperpart 55b of the second lens group 51b. Referring to FIG. 5B, if thefirst lens group 51a and the second lens group 51b are moved furthertoward the image surface for varying the magnification for a wider angleof view, the luminous flux is almost totally eclipsed by the upper part55b of the second lens group 51b to render shooting impossible. In otherwords, when the image plane is in its full size, the wide-angle endshown in FIG. 5B is the zoom position of the widest possible angle ofview.

On the contrary, in a case where a special shooting is to be performedwith the image plane size reduced as shown in FIG. 5C, the reduction insize of the image plane enables the luminous flux which is incident onthe peripheral part 2b of the image plane and is eclipsed by the secondlens group 51b in the case of FIG. 5B to pass through the lens group 51bwithout being eclipsed. In other words, with the image plane sizereduced as shown in FIG. 5C, the luminous flux L55c incident on theperipheral part 2b of the image plane is allowed to pass through withoutbeing eclipsed by the upper part 55b of the lens group 51b even when thelens group 51b is moved further toward the image surface from itsposition shown in FIG. 5B.

By utilizing this optical property, the second embodiment is arranged tobe capable of moving the power varying part of the photo-taking lens(zoom lens) by an interlocking mechanism to a further extent on thewide-angle side when the image plane is in a smaller size than when theimage plane is in a larger size. The zooming range is thus expanded onthe wide-angle side for an ultra-wide angle of view. In other words,when the image plane size is reduced by the image plane size varyingmeans, the maximum movable amount of the power varying part of thephoto-taking lens 51 is increased in response to the action of the imageplane size varying means. In a case where, for example, a panoramiceffect is to be attained in the special shooting mode, the image planeis laterally expanded for a wider angle of view.

In the panorama mode, the image plane which is in the full size of the35 mm film is vertically blocked in part from light on the upper andlower sides of the image plane. Therefore, the size of the image planein the lateral direction thereof remains almost completely unchanged.With the angle of view widened in the panorama mode, therefore, theangle of view is widened in the lateral direction to further thepanoramic effect. This effect is attainable not only from use of thezoom lens of the type shown in FIGS. 5A, 5B and 5C but also from a zoomlens of the ordinary four group type or the like.

FIG. 6 shows the system arrangement of this embodiment. Referring toFIG. 6, a control circuit 61 includes a microcomputer or the like. Azoom motor driving circuit 62 is arranged to drive and control a motor63. The motor 63 is arranged to drive the lens groups 51a and 51b of apower varying part in a known manner. Focal length detecting means 64 isarranged to detect a focal length of the whole system (a zoom position)obtained by the magnification (power) varying action of the powervarying part. The control circuit 61 is provided with switches S1, S2and S3.

The switch S1 is arranged to be turned on in setting the embodiment in aspecial shooting mode, such as a panorama mode. The switch S2 isarranged to be turned on in shifting the power varying part, forexample, toward a telephoto end position. The switch S3 is arranged tobe turned on, for example, in shifting the power varying part toward awide-angle end position.

This embodiment is arranged to have a normal image plane size (or a fullimage plane size) when the switch S1 is in an off-state. With the imageplane in the normal (full) size, the focal length detecting means 64detects a magnification (power) varying range when either the switch S2or the switch S3 is turned on. The power varying action is performed,with the image plane in the normal size, by causing the zoom motordriving circuit 62 to drive the motor 63 within the normal power varyingrange up to a telephoto end or wide-angle end position.

When the switch S1 is in an on-state to have the embodiment in thepanorama mode in which the image plane is changed from its normal size,the lens is driven toward the wide-angle end position if the switch S3continues to be in the on-state. Therefore, in that instance, thecontrol circuit 61 detects from the focal length detecting means 64 thewide-angle end zoom position for the full size image plane and, afterthat, causes the power varying part to be driven from the wide-angle endzoom position detected further toward a wider angle position. In otherwords, the power varying part is driven toward a wider angle position bythe zoom motor driving circuit 62 and the motor 63 to perform its powervarying action for an ultra-wide-angle end position set for the panoramamode.

Further, in a case where the switch S2 turns on with the switch S1 inits on-state, telephoto driving takes place. In that instance, the powervarying action is performed up to the normal telephoto end position likewhen the switch S1 is in its off-state.

In the second embodiment described above, in attaining various specialshooting effects by varying the image plane size on the photosensitivesurface, such improvements in optical specifications that have beendifficult to attain for the photo-taking lens with the image plane inthe larger size, such as shortening the nearest shootable objectdistance, expanding the shooting angle of view to a wider angle (for anultra-wide angle), in a case where the photo-taking lens is a zoom lens,are attainable with the applicable component elements set as describedabove. Therefore, in accordance with the arrangement of the embodiment,the camera can be provided with image plane size varying means whichpermits the above-stated improvements in optical specifications.

Next, the optical states of the zoom lens shown in FIGS. 5A, 5B and 5Care described with mathematical expressions as follows:

Assuming that the longest length of the diagonal line of the image plane(a normal image plane) is D, the length of the diagonal line of an imageplane reduced by the image plane size varying means is d, the normalshortest focal length of the photo-taking lens obtained when thediagonal length of the image plane is D is F and the focal length of thephoto-taking lens obtained when the diagonal length of the image planeis d is f, there are obtained the following relations: ##EQU1## whereinθ1 represents an angle of view obtained when the diagonal length of theimage plane is D, and θ2 represents an angle of view obtained when thediagonal length of the image plane is d.

No conspicuous wide-angle shooting effect is attainable even if theimage plane size is changed, if the rate of change in the diagonallength "d/D" and the rate of expansion of the shootable range (the rateof change in focal length on the wide-angle side) "f/F" are equal toeach other. Further, if the rate of change in the diagonal length of theimage plane "d/D" is smaller than the rate of expansion of the shootablerange "f/F", it is more impossible to attain the wide-angle shootingeffect. In such a case, therefore, it is meaningless to change the sizeof the image plane.

In order to attain a conspicuous wide-angle shooting effect by makingthe image plane size smaller than the normal size, the angle of view θ2must be larger than the angle of view θ1. Hence, from the formula (1), acondition for attaining any conspicuous wide-angle shooting effect canbe expressed as follows:

    tan θ1<tan θ2                                  (2)

The following formula is derivable from the above-stated formulas (1)and (2): ##EQU2##

It is, therefore, necessary to satisfy the formula (3) for attaining anyconspicuous wide-angle shooting effect when changing the size of theimage plane.

When the size of the image plane is changed, the image plane sizevarying means and the power varying means of the photo-taking opticalsystem of the embodiment are controlled in association with each otherin such a way as to satisfy the formula (3). In addition to this, inshooting with the image plane size changed (reduced), the power varyingoptical system of the embodiment is brought into an ultra-wide angleposition where a wider angle than a normally maximum wide angle isobtained for attaining more conspicuous wide-angle effect than theconventional camera, so that a conspicuous wide-angle shooting effectwhich is hardly attainable with the conventional panorama shooting typecamera can be attained.

With respect to the arrangement for shifting the photo-taking opticalsystem from the normally maximum wide-angle position further to theultra-wide angle position, the optical system may be arranged to includean auxiliary lens 72 which is arranged, separately from a photo-takinglens 71 as shown in FIGS. 7A and 7B, to be inserted into the opticalaxis of the photo-taking lens 71.

FIG. 7A shows the auxiliary lens 72 as in its normal position in which anormally maximum wide-angle state is obtained with the auxiliary lens 72not inserted in the optical axis in the rear of the photo-taking lens71. In this case, the diagonal length of the image plane is at itsmaximum value D. In the case of FIG. 7B, the diagonal length of theimage plane is shortened to a value d by the mask 4 of the image planesize varying means. In that case, the auxiliary lens 72 is inserted inthe rear of the photo-taking lens 71 in response to the change in theimage plane size, and the photo-taking lens 71 is set in its maximumwide-angle position.

FIGS. 8A to 8D show another example of the optical system arrangement.In this instance, an auxiliary lens 82 which has a negative refractivepower is arranged to be insertable into the optical axis of a mainoptical system. The zoom lens of the main optical system includes afirst lens group 81a (focusing lens) which has a positive refractivepower, a second lens group 81b (variator lens) which has a negativerefractive power, a third lens group 81c (image surface compensationlens) which has a negative refractive power, a fourth lens group 81dwhich has a positive refractive power, and a fifth lens group 81e whichhas a positive refractive power. A zooming action is performed bydifferentially moving the second lens group 81b and the third lens group81c as shown in FIGS. 8C and 8D. Macro-shooting is possible by slightlymoving the third lens group 81c with the second lens group 81b fixed atthe wide-angle end of zooming.

In the macro-shooting mode, as shown in FIG. 8B, with the third lensgroup 81c moved toward the object at the wide-angle end of the zoom lenswhich is arranged as described above, the auxiliary lens 82 is insertedin between the second lens group 81b and the third lens group 81c tocorrect the shooting distance to the normal shooting distance (based oninfinity distance), and the diagonal length of the image plane isshortened to the length d by means of the mask 4 of the image plane sizevarying means, as shown in FIG. 8A.

FIGS. 9A and 9B show a further example of the optical systemarrangement. In this case, an auxiliary lens 94 is inserted into a mainoptical system (image forming optical system). Referring to FIG. 9B, theauxiliary lens 94 is an afocal wide-angle converter lens. The auxiliarylens 94 includes a front lens group 94a which has a negative refractivepower and a rear lens group 94b which has a positive refractive power.The main optical system, i.e., the image forming optical system,consists of a monofocal lens 91. When the image plane is in a standard(normal) size having the diagonal length D, the monofocal lens 91 of theimage forming optical system has the focal length F. When the imageplane size is changed to change the diagonal length from the length D tothe length d which is shorter than the length D, the afocal wide-angleconverter lens 94 which is the auxiliary lens is inserted in the opticalaxis in front of the monofocal lens 91.

FIG. 10 is a block diagram showing the control system arrangement of aninterchangeable-lens type camera to which this invention is applied.

Referring to FIG. 10, the illustration includes a camera body 100, aninterchangeable lens 110 which is detachably mounted on the camera body110, control means 101 which includes a microcomputer or the like, imageplane size varying means 102, detecting means 103 for detecting thestate of the image plane size varying means 102 obtained at anyarbitrary point of time, an operation member 104 which is arranged to bemanually operated by the operator for changing the image plane size, anddriving means 105 connected to the image plane size varying means 102.This driving means 105 is employed only in a case where the image planesize varying means 102 is a mechanical means. If the image plane sizevarying means 102 is composed of a liquid crystal, the image plane sizevarying means 102 is controlled directly by the control means 101.Optical system driving means 111 is arranged to drive a power varyingoptical system and an image forming optical system. Optical systemcontrol means 112 is arranged to control the optical system drivingmeans 111. Optical system detecting means 113 is arranged to detect thepositions of the power varying optical system and the image formingoptical systems.

With the camera arranged as described above according to this invention,when the operator of the camera operates the operation member 104 tocause the size of the image plane to be varied by the image plane sizevarying means 102, the image plane varying state is detected by thedetecting means 103. The detecting means 103 then outputs a detectionsignal. The detection signal is taken in by the control means 101. Thecontrol means 101 causes the optical system control means 112 to havethe lens of the power varying optical system driven by the opticalsystem driving means 111 in such a way as to satisfy the above-statedformula "d/D>f/F". When the position of the power varying optical systemand that of the image forming optical system are detected by thedetecting means 113, the output of the detecting means 113 is fed backto the optical system control means 112. Then, the power varying opticalsystem and the image forming optical system are controlled accordingly.

In a case where the lens of the power varying optical system is shiftedfrom the normally maximum wide-angle position further to an ultra-wideangle position without varying the size of the image plane by the imageplane size varying means 102, this change in position is detected by theoptical system detecting means 113. The control means 101 then obtainsthe detection output of the detecting means 113. Upon receipt of thedetection output, the control means 101 causes the driving means 105 todrive the image plane size varying means 102 in such a way as to satisfythe above-stated formula.

Further, while the foregoing description of embodiments relates only tocameras, it goes without saying that this invention is applicable alsoto other optical apparatuses such as observation equipments, projectorsand so on. Further, while each of the lenses which is shown as a singlelens in the accompanying drawings for the sake of illustration actuallyconsists of a plurality of lens elements in many cases.

What is claimed is:
 1. A camera comprising:a) varying means for varyingan image pickup area from a first size to a second size, the second sizehaving a shorter diagonal length than a diagonal length of the firstsize; and b) objective lens means for varying a focusable minimum objectdistance when the image pickup area changes from the first size to thesecond size, said objective lens means having a shorter minimum objectdistance at the second size than at the first size.
 2. A cameraaccording to claim 1, further comprising automatic distance detectingmeans arranged to output a detection value, and wherein said objectivelens means comprises means for allowing said objective lens means to befocused on an object located at a distance closer than a minimum valueof a focusable range set for the first size, according to the detectionvalue, when said varying means varies the image pickup area to thesecond size.
 3. An optical apparatus comprising:a) image forming opticalmeans for forming an image, said image forming optical means having amagnification that is variable from a first state to a wide angle state;b) image plane size varying means for varying a size of an image plane;and c) control means for controlling said image forming optical means toallow shifting of said image forming optical means from the wide anglestate to a wider angle state in association with a change of the size ofthe image plane, wherein, when "D" is a maximum diagonal length of theimage plane, "d" is a diagonal length of the image plane shortened bythe change of the size of the image plane, "F" is a shortest focallength of said image forming optical means normally obtainable when theimage plane has the maximum diagonal length and "f" is the shortestfocal length of said image forming optical means obtainable when thediagonal length of the image plane becomes d, said control meanscontrols shifting of said image forming optical means to the wider anglestate so that the following relation is satisfied: d/D>f/F.
 4. Anapparatus according to claim 3, wherein said image forming optical meanscomprises a lens unit that is movable in the direction of an opticalaxis to vary the magnification of said image forming optical means. 5.An apparatus according to claim 3, wherein said image forming opticalmeans comprises an auxiliary lens that is insertable into an opticalpath of said image forming optical means to vary the magnification ofsaid image forming optical means.
 6. An apparatus according to claim 3,wherein said image forming optical means comprises a lens unit that ismovable in the direction of an optical axis to vary the magnification ofsaid image forming optical means and an auxiliary lens that isinsertable into an optical path of said image forming optical means toplace said image forming optical means in a wider angle state.
 7. Acamera comprising:a) varying means for varying an image pickup area froma first size to a second size, the second size having a shorter diagonallength than a diagonal length of the first size; and b) objective lensmeans for varying zooming range when the image pickup area changes fromthe first size to the second size, said objective lens means having abroader zooming range at the second size than at the first size.
 8. Acamera according to claim 7, wherein said objective lens means has azooming range expanding to the wide angle side of view at the secondsize.